Active Flow Control Strategy of Laminar Separation Bubbles Developed over Subsonic Airfoils at Low Reynolds Numbers

Laminar separation and transition have significant effects on aerodynamic characteristics of the wing under the condition of low Reynolds numbers. Using the flow control methods to delay and eliminate laminar separation has great significance. This study uses the method combined with water tunnel test and numerical calculation to research the effects of suction flow control on the flow state and aerodynamic force of the wing at low Reynolds numbers. The effects of suction flow rate and suction location on laminar separation, transition and aerodynamic performance of the wing are further researched. The results of the research show that, the suction can control laminar separation and transition effectively, when the suction holes are in the interior of the separation bubble, and close to the separation point, the suction has the best control effect. When the Reynolds number is Re = 3.0 × 105, the suction flow control can make the lift-to-drag ratio of the wing increase by 8.62%, and the aerodynamic characteristics of the wing are improved effectively.

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Active Control of Laminar Separation: Simulations, Wind Tunnel, and Free-Flight Experiments

Aerospace ◽

10.3390/aerospace5040114 ◽

2018 ◽

Vol 5 (4) ◽

pp. 114 ◽

Cited By ~ 2

Author(s):

Andreas Gross ◽

Hermann Fasel

Keyword(s):

Wind Tunnel ◽

Active Control ◽

Active Flow Control ◽

Reynolds Numbers ◽

Scale Model ◽

Separation Control ◽

Free Flight ◽

Laminar Separation ◽

Separation Bubbles ◽

Laminar Separation Bubbles

When a laminar boundary layer is subjected to an adverse pressure gradient, laminar separation bubbles can occur. At low Reynolds numbers, the bubble size can be substantial, and the aerodynamic performance can be reduced considerably. At higher Reynolds numbers, the bubble bursting can determine the stall characteristics. For either setting, an active control that suppresses or delays laminar separation is desirable. A combined numerical and experimental approach was taken for investigating active flow control and its interplay with separation and transition for laminar separation bubbles for chord-based Reynolds numbers of Re ≈ 64,200–320,000. Experiments were carried out both in the wind tunnel and in free flight using an instrumented 1:5 scale model of the Aeromot 200S, which has a modified NACA 643-618 airfoil. The same airfoil was also used in the simulations and wind tunnel experiments. For a wide angle of attack range below stall, the flow separates laminar from the suction surface. Separation control via a dielectric barrier discharge plasma actuator and unsteady blowing through holes were investigated. For a properly chosen actuation amplitude and frequency, the Kelvin–Helmholtz instability results in strong disturbance amplification and a “roll-up” of the separated shear layer. As a result, an efficient and effective laminar separation control is realized.

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